In the United States, cataract surgery is the most frequently performed surgical procedure among 30 million Medicare beneficiaries at an estimated cost of $3.5 billion per year. In the Baltimore Eye Survey, cataract is reported as the leading cause of blindness in those over the age of 40, and to be four times more common in African-Americans than in Caucasian-Americans. In the world, cataract is the leading cause of blindness. The proposed research is designed to take a significant step toward reducing blindness resulting from cataract. To evaluate the effectiveness of preventative therapy designed to delay or prevent cataract formation, new sensitive markers of early cataract development and progression need to be identified. This need is specifically recognized and reflected in Objective 1 of the Report of the Lens and Cataract Panel in: Vision Research, A National Plan: 1999-2003. Objective 1 of the NEI report is to: "Determine if there are novel markers that differentiate the normal aging process from the diseased (cataractous) state." To meet objective 1, the Report identifies the need for the development of "morphological and optical markers that can be visualized by noninvasive techniques." The specific aims of the resubmission are to demonstrate that: wavefront sensing can quantify the optical aberrations and local scattering properties of early cataract formation; wavefront sensing can differentiate the normal aging process from the cataractous state; wavefront sensing has the accuracy and precision to be an effective monitoring tool in longitudinal studies of new therapy designed to delay, prevent, or slow cataract formation and progression. These specific aims will be accomplished by modifying Hartmann/Shack wavefront sensor technology to quantify the optical aberrations and local scattering properties of eyes with early cataract and eyes of normals in the 4th, 5th and 6th decades of life.